In many extra-high frequency technology applications, in particular for millimetric wave technology, it is necessary to inject a wave which has been carried in a microstripline into a waveguide, and vice versa. In this case, the junction should be as free of reflections and losses as possible. This junction ensures, within a limited frequency range, that the impedances between the waveguide and the stripline are matched to one another, and that the field pattern of the first waveguide type is transferred to the field pattern of the other waveguide type.
Microstripline/waveguide junctions are known, for example, from DE 197 41 944 A1 or U.S. Pat. No. 6,265,950 B1.
DE 197 41 944 A1 describes an arrangement in which the microstripline is applied to the upper face of the substrate (FIG. 1). An end surface of the waveguide HL is fitted on the lower face of the substrate S. The substrate S has an aperture D in the area of the waveguide HL. The aperture D corresponds essentially to the cross section of the waveguide HL. A coupling element (not illustrated) is arranged on the microstripline ML and projects into the aperture D. The aperture D is surrounded on the upper face of the substrate S by a screening cap SK, which is electrically connected by means of electrically conductive drilled holes (via holes) VH to the metallization RM on the lower face of the substrate S.
This arrangement has the disadvantage that the printed circuit board must be mounted conductively on a prepared mounting plate containing the waveguide HL. In addition, a precision manufactured shielding cap SK, which is mechanically positioned with precision and must be applied conductively, is required. The production of this arrangement is time-consuming and costly due to the large number of different types of processing steps. Further disadvantages result from the large amount of space required as a result of the waveguide being arranged outside the printed circuit board.
In the arrangement described in U.S. Pat. No. 6,265,950 B1 for a junction between a microstripline and a waveguide, the substrate with the microstripline applied to it projects into the waveguide. One disadvantage of this arrangement is the integration of the waveguide in a printed circuit board environment. The waveguide can be arranged only on the boundary surfaces of the printed circuit board (substrate). The waveguide cannot be integrated within the printed circuit board, because of the costly preparation of the printed circuit board.
The object of the invention is to specify an arrangement for a junction between a microstripline and a waveguide, which can be produced easily and at low cost and which occupies only a small amount of space.
The arrangement according to the invention for a junction between a microstripline and a waveguide comprises:                a microstripline which is fitted on the upper face of a dielectric substrate,        a waveguide which is fitted on the upper face of the substrate and has an opening on at least one end surface and has a structure which is in the form of a step or steps in the area of the opening on one side wall and is conductively connected in at least one part to the microstripline, and wherein one side wall of the waveguide is a metallized layer formed on the substrate,        a cutout which is formed in the metallized layer and into which the microstripline projects,        rear-face metallization which is formed on the rear face of the substrate, and        electrically conductive via holes between the metallized layer on the upper face of the substrate and the rear-face metallization, which surround the cutout.        
One advantage of the arrangement according to the invention is that the microstrip/waveguide junction can be produced easily and at low cost. The production of the junction requires fewer components than the prior art. A further advantage is that the implementation of the waveguide in the printed circuit board environment need not be at the edge of the printed circuit board as in the case of the U.S. Pat. No. 6,265,950 but can be provided at any desired point on the printed circuit board. The arrangement according to the invention thus occupies little space.
The waveguide is advantageously a surface mounted device. The waveguide part is for this purpose fitted to and conductively connected to the printed circuit board from above in a single fitting step. The connection of the waveguide to the junction can thus be integrated in known component placement methods. This saves manufacturing steps, thus reducing the production costs and time.